Strict anti-pollution codes have been enforced in order to suppress the emission of various pollutants into the atmosphere. In order to suppress the emission of nitrogen oxides (NO.sub.x), there has been devised and successfully demonstrated a denitrification system wherein the effluent is brought into contact with catalyst in the presence of NH.sub.3. Such denitrification systems must be increased in capacity proportionally to the increase in capacity of a pollution source such as a boiler furnace. As a result, a large amount of catalyst is required. For instance, in order to denitrate the effluent at a rate of 1,000,000 Nm.sup.3 /h, the catalyst amounting to about 200 m.sup.3 is required.
The effective lifetime of catalyst is in general from one to four years and the replacement of catalyst is permitted only during the short periodic inspections of for instance a steam boiler. Furthermore, the catalyst blocks or the like, which are easily susceptible to cracking, must be handled with special care.
In order to facilitate the handling of catalyst, there has been devised and demonstrated a method wherein a plurality of catalyst blocks or the like are packed within a case with a suitable strength. The case has two opposed open ends, through which the catalyst blocks or the like are merely inserted into the case. Furthermore such cases packed with catalyst blocks or the like are merely stacked or piled up in a denitrification reactor so that spaces are left between the adjacent cases and the effluence flows through these spaces without passing through the catalyst blocks or the like, thereby resulting in the decrease in denitrification efficiency. Moreover, the catalyst blocks or the like packed in the cases are frequently susceptible to cracking and fracture because of the vibration or impact during the handling.
The catalyst blocks or the like must be packed into a case in such a way that the gas-tightness may be ensured between the adjacent catalyst blocks or the like and between the catalyst blocks or the like and the case.
However it is extremely difficult to fabricate the catalyst blocks or the like into such a shape that the gas-tightness may be ensured between the stacked or piled up catalyst blocks. If this were possible, it would be more difficult to insert or pack the catalyst blocks into a case in such a gas-tight manner as described above. Furthermore, as described above, the catalyst blocks or the like are very fragile so that it will take an inhibitively long time to pack them into a case. Sealing the spaces left between the stacked or piled up catalyst blocks or the like would be also an inhibitively time- and labor-consuming operation.
A further problem of the cases packed with the catalyst blocks or the like is that because of the limited strength of the cases, there is a limit to the number of cases stacked in the reactor. As a result, the prior art catalyst case system is not adapted for use in a denitrification reactor with a large capacity.
Accordingly, one of the objects of the present invention is to provide a denitrification reactor wherein catalyst cells may be loaded or off-loaded within a short time and wherein the catalyst cells are packed with the catalyst blocks and are stacked in the reactor vessel in such a gas-tight manner that the effluent may be completely prevented from bypassing the catalyst blocks.
The present invention will become apparent from the following description of one preferred embodiment thereof taken in conjunction with the accompanying drawings.